stdlib/erand48_r.c

   1 /* Copyright (C) 1995-2022 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <ieee754.h>
  19 #include <stdlib.h>
  20 #include <limits.h>
  21
  22
  23 int
  24 __erand48_r (unsigned short int xsubi[3], struct drand48_data *buffer,
  25              double *result)
  26 {
  27   union ieee754_double temp;
  28
  29   /* Compute next state.  */
  30   if (__drand48_iterate (xsubi, buffer) < 0)
  31     return -1;
  32
  33   /* Construct a positive double with the 48 random bits distributed over
  34      its fractional part so the resulting FP number is [0.0,1.0).  */
  35
  36   temp.ieee.negative = 0;
  37   temp.ieee.exponent = IEEE754_DOUBLE_BIAS;
  38   temp.ieee.mantissa0 = (xsubi[2] << 4) | (xsubi[1] >> 12);
  39   temp.ieee.mantissa1 = ((xsubi[1] & 0xfff) << 20) | (xsubi[0] << 4);
  40
  41   /* Please note the lower 4 bits of mantissa1 are always 0.  */
  42   *result = temp.d - 1.0;
  43
  44   return 0;
  45 }
  46 weak_alias (__erand48_r, erand48_r)